Forage Quality Interpretations

Forage Quality Interpretations
EXTENSION FACTS
Oklahoma Cooperative Extension Service • Division of Agricultural Sciences and Natural Resources
F-2117
John Caddel
Forage Extension Agronomist
Earl Allen
Director, Soil, Water, and Forage Analytical Laboratory
High quality forages are crucial for the livestock
industry. They furnish essential energy, proteins, vitamins, minerals, and fibers. In fact, diets of most domestic livestock consist principally (if not entirely) of forages.
Compared to cereal grains and pulses (dry, edible
legume seeds), quality factors of forages vary greatly
among species and can even vary within a single forage
species. Forage quality is dependent upon species
mixtures, stage of maturity, growing environment, soil
fertility levels, and forage harvesting. For these reasons, evaluating the quality of forages for the production of meat, milk, and wool is complex.
The best single measure of forage quality is
animal productivity. Animal productivity is in turn
affected by forage intake, digestibility, and nutrient
utilization efficiency.
Forages have historically been evaluated onphysical factors which include color, leafiness, maturity,
smell, softness, and purity. These factors are still
important in assessing forage quality, but they remain
very subjective and difficult to standardize.
Chemical analyses are useful tools in estimating
certain forage quality factors. Direct chemical tests are
usually accurate, but are somewhat slow and must be
conducted in standard laboratory conditions. During
the last decade, Near Infrared Reflectance Spectroscopy (NIRS) has been improved and has become
popular. NIRS results are highly correlated to direct
chemical procedures for alfalfa, when properly calibrated. NIRS units are relatively portable, fast, and
precise, but sometimes results are not accurate, when
inadequately calibrated.
Principal forage analysis values used in ration
formulations are: Crude Protein (CP); Acid Detergent
Fiber (ADF); and Neutral Detergent Fiber (NDF). ADF
estimates forage digestibility, and NDF provides an
estimate of forage intake for some forages. Crude
protein, estimated from total nitrogen concentration, is
Figure 1. Forage Quality Properties Determined by
Laboratories.
always important in rations because it is usually the
highest-priced nutrient.
Forage quality analyses (using direct chemical
analysis, or NIRS) normally measure four different
attributes: %Total Nitrogen, %ADF, %NDF, and %Moisture. Sometimes the concentration of certain minerals
(e.g., calcium and phosphorus) is also determined.
Other properties listed in forage analysis reports are
mathematically derived from the measured attributes.
These usually include digestible protein (DP), total
digestible nutrients (TDN), net energy (NE), digestible
dry matter (DDM), dry matter intake (DMI), and relative
feed value (RFV), as shown in Figure 1. Both measured
and derived values are used by hay buyers and sellers
to estimate the value of forages.
Conducting chemical analyses and assessing physical characteristics by sight, smell, and feel are the best
ways to develop an overall evaluation of forage. This
fact sheet describes some chemical factors in forage
analysis and how they can be used. Other OSU
Cooperative Extension Facts are available at County
Extension Offices. Hay Judging (No. 2588) concentrates on assessment of physical characteristics and
their relative importance for various livestock. Utilization & Value of Alfalfa in Dairy Rations (No. 4013)
emphasizes the value of different qualities of alfalfa hay
for dairies.
Oklahoma2117.1
State University
Example: If ADF
% DDM
= 28%, then
= 88.9 - (0.779 X 28)
= 88.9 - 21.8
= 67.1%
The formula for estimatingDry Matter Intake (DMI),
as % of animal body weight from NDF, is :
% DMI = 120
% NDF
Relative Feed Value
Both buyers and sellers continue to seek common
means of estimating hay quality in terms of its value as
a feed for livestock. Relative Feed Value (RFV) is
gaining acceptance as the best single value to estimate
alfalfa forage quality for dairy cattle. Hay buyers want
to know RFV, making it a valuable marketing tool.
That should not imply RFV is the only important
forage quality estimator. For example, RFV does not
say anything about protein concentration or physical characteristics. Protein and physical characteristics must be evaluated along with RFV for a complete
assessment of forage quality.
The formula for estimating RFV from Digestible Dry
Matter (DDM) and Dry Matter Intake (DMI) is:
RFV = (% DDM) X (% DMI) X (0.775)
DDM and DMI are derived from ADF and NDF, respectively. Laboratories may use slightly different formulae
to calculate DDM and DMI, but final estimated values
are similar.
The common formula for estimatingDigestible Dry
Matter (DDM) from ADF is:
% DDM = 88.9 - (0.779 X %ADF)
Example: If NDF = 38%, then
% DMI = 120
38
= 3.15 % of body weight.
From the above examples, a forage with ADF =
28% and NDF = 38% would have RFV of 164.
RFV = (67.1) X (3.15) X (0.775) = 164.
Table 1 eliminates the tedious calculations of RFV.
RFV can be determined by locating the percent NDF
along the top and percent ADF along the left side.
What does RFV = 164 mean? RFV has no specific
nutritional meaning and is used only as an index of the
Table 1. Relative Feed Values (RFV)* for selected values of Acid Detergent Fiber (ADF) and Neutral Detergent Fiber (NDF).
ADF,
%
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
30
32
34
36
38
40
227
225
223
220
218
215
213
213
211
209
206
204
202
200
197
195
201
198
196
194
192
190
188
186
184
181
179
189
187
185
183
181
179
177
175
173
171
169
167
165
179
178
176
174
172
170
168
166
164
162
160
159
157
155
153
171
169
167
165
163
161
160
158
156
154
152
151
149
147
145
143
142
NDF, %
42
162
161
159
157
155
154
152
150
149
147
145
143
142
140
138
137
135
133
131
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44
46
48
50
52
54
56
155
153
152
150
148
147
145
143
142
140
139
137
135
134
132
130
129
127
125
124
122
148
147
145
144
142
140
139
137
136
134
133
131
129
128
126
125
123
121
120
118
117
115
114
142
141
139
138
136
135
133
132
130
129
127
125
124
122
121
119
118
116
115
113
112
110
109
107
106
136
135
134
132
131
129
128
126
125
123
122
120
119
118
116
115
113
112
110
109
107
106
105
103
102
100
99
131
130
128
127
126
124
123
121
120
119
117
116
114
113
112
110
109
107
106
105
103
102
101
99
98
96
95
94
92
126
125
124
122
121
120
118
117
116
114
113
112
110
109
108
106
105
103
102
101
99
98
97
95
94
93
91
90
89
87
122
121
119
118
117
115
114
113
111
110
109
108
106
105
104
102
101
100
99
97
96
95
93
92
91
89
88
87
86
84
relative value of a forage. It combines into a single
number the digestibility of the forage and an estimate of how much forage will be consumed.
The general relation between forage maturity and
four quality estimators is illustrated in Table 2. As
maturity advances, crude protein and RFV generally
decrease, and ADF and NDF increase.
To establish a base-point to better determine where
RFV’s rate on the quality scale, it can be noted that an
ADF of 41% and an NDF of 53% would relate to an RFV
of 100. The RFV of alfalfa hay harvested at full bloom
is expected to be about 100 (Table 2). The higher the
RFV, the higher the quality of the forage.
Forage quality analyses are no better than the
procedures used to obtain the samples.
Samples must represent a particular lot of
forage (hay, silage, pasture, etc.). OSU
Extension Facts No. 2589, Collecting Forage
Samples for Analysis, outlines good ways to
obtain representative forage samples for
analysis.
pass through the rumen without being absorbed —
essentially wasted.
There is no single way to assign dollar values to
forages based strictly on forage analysis. Table 3
illustrates the relationship among various quality factors. These grade classes were developed by the
American Forage and Grassland Council and are accepted by many forage buyers and sellers.
If alfalfa hay with an RFV of 160 is the only forage
fed to lactating dairy cattle, then higher RFV’s would
have no additional value. However, dairymen sometimes mix very high quality forages with inferior forages
to arrive at the desired forage digestibility and intake. In
such cases, forages with RFV’s higher than 150 have
additional value and should demand higher prices.
When forages are fed to animals in limited quantities, such as supplements for cow-calf herds and dry
cows, the importance of RFV changes. The herdsman
limits forage intakeby providing only a certain quantity
per animal, and the NDF of the forage becomes less
important. Digestibility (estimated by ADF) and CP are
the main quality factors to consider in these situations.
Table 2. Typical Crude Protein (CP), Acid Detergent Fiber
(ADF), Neutral Detergent Fiber (NDF) and Relative Feed
Values (RFV) for alfalfa hay at different maturities.
Stage of Maturity
Bud
Early Bloom
Mid bloom
Full Bloom
%CP
%ADF
%NDF
RFV
25
23
19
16
28
30
35
41
38
40
46
53
164
152
125
100
Using Forage Quality Information
A general rule-of-thumb to help remember forage
quality analysis factors is “20-30-40”. High-producing
dairy cows need hay with at least 20% CP, less than
30% ADF, and less than 40% NDF. This is equivalent
to just over an RFV of 150. Forages with better CP,
ADF, and NDF values are not necessarily better for milk
production. When CP is more than 25%, ADF is less
than 25%, and/or NDF is less than 35%, many nutrients
Table 3. Market hay grades for legumes, legume-grass mixtures, and grasses — American Forage & Grassland Council,
Hay Marketing Task Force.
Description
Grade
Species and Stage
%CP
%ADF
%NDF
%DDM
RFV
Prime
Legume, pre-bloom
>19
<31
<40
>65
>151
1
Legume, early bloom,
20% grass-vegetative
17-19
31-35
40-46
62-65
125-151
Legume, mid-bloom,
30% grass-early-head
14-16
36-40
47-53
58-61
101-124
Legume, full bloom,
40% grass-headed
11-13
41-42
54-60
56-57
86-100
Legume, full bloom,
50% grass-headed
8-10
43-45
61-65
53-55
77-85
<8
>45
>65
<53
<77
2
3
4
Fair
Grass-headed and/or
rain-damaged
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Care should be exercised when applying RFV to
forages other than alfalfa, because most of the calibration work and formulae for calculating digestibility and
intake are currently based on alfalfa hay. Consequently, underlying assumptions may not apply to certain other forages. As more information is accumulated
for other forages, RFV’s (perhaps with different conversion factors) can be calculated for them.
Establishing market grades of forages similar to
those set up for many agricultural products has not
received wide spread acceptance. One reason is
variation from one type of forage to another. The
American Forage and Grassland Council’s Hay Marketing Task Force developed the grades and descriptions shown in Table 3. This grading system works well
for a single forage species utilized for a single purpose.
For example dairymen feeding alfalfa hay can use
these grades. Depending upon supply and demand at
a particular time during the year, most lots of “prime”
alfalfa hay may be sold for a fairly narrow range of
prices. The same could be said for other grades.
The system is more difficult to use for feedlot
operators using a grass hay such as sorghumsudangrass or bermudagrass. Prime and grade 1 may
not be needed because the nutritive value of grade 2 or
3 may meet the roughage needs of feeders. Therefore,
prime and grade 1 may be of no added value. Another
complication enters with grass-legume mixtures.
What Affects Forage Quality?
Almost everything can affect forage quality in one
way or another. Soil moisture and soil fertility, while the
forage is growing, are important. Generally, the better
the growing conditions, the higher the forage quality.
With good growing conditions, the most important
factor affecting forage quality is stage of growth at
harvest. More mature forage is less nutritious. Older
plants generally have a lower proportion of leaves and
a higher proportion of stem material (highly indigestible fiber). Young tender stems, leaves, and flowers
provide the highest quality forage.
Forage producers and users recognize that quality
does not improve after harvesting. The harvesting
process can, however, reduce forage quality. For
example, leaf loss caused by rain or excessive raking
lowers forage quality. Baling hay too wet can cause
excessive heating and mold to develop.
Forage quality can also be reduced during storage.
Uncovered hay stored outside loses nutrients by the
leaching action of rain. When hay becomes wet (from
rain or absorbing moisture from the soil) it can rot, even
though it was dry when baled (OSU Extension Facts No.
1716).
In summary, high-quality forage is the end product of good growing conditions, correct timing of
harvest, and proper handling from harvesting to
utilization.
OSU Extension Facts and Current Reports
for Improving Forage Quality
Hay Judging. No. 2588
Utilization & Value of Alfalfa in Dairy Rations. No. 4013
Weed Control in Alfalfa. No. 2761
Collecting Forage Samples for Analysis. No. 2589
Round Bale Hay Storage. No. 1716
How to Get a Good Soil Sample. No. 2207
OSU Soil Test Interpretations. No. 2225
Alfalfa Varieties for Oklahoma. No. 2106
Alfalfa Stand Establishment. No. 2089
Blister Beetles and Alfalfa. No. 2072
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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Charles B. Browning, Director of Oklahoma
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